From 5f1f0e1f7b786e5c3c9d8a53df3e74ce44b0dd98 Mon Sep 17 00:00:00 2001
From: Val <val@soft.fish>
Date: Fri, 31 May 2024 16:19:22 -0500
Subject: [PATCH] game-life: Implement Conway's Game of Life

---
 .gitignore  |  1 +
 Cargo.lock  |  7 ++++
 Cargo.toml  |  6 ++++
 src/lib.rs  | 98 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/main.rs | 26 ++++++++++++++
 5 files changed, 138 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Cargo.lock
 create mode 100644 Cargo.toml
 create mode 100644 src/lib.rs
 create mode 100644 src/main.rs

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..ea8c4bf
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+/target
diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..9180d4a
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "game-life"
+version = "0.1.0"
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..77a9e17
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "game-life"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..f2a639d
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,98 @@
+//! Conway's Game of Life on a torus
+
+pub fn rem(lhs: isize, rhs: usize) -> usize {
+    lhs.rem_euclid(rhs as _) as usize
+}
+
+pub struct Board<const X: usize, const Y: usize> {
+    pub front: Box<[[u8; X]; Y]>, // The display buffer
+    pub back: Box<[[u8; X]; Y]>, // These are heap allocated to make buffer swaps a pointer operation
+}
+
+impl<const X: usize, const Y: usize> Default for Board<X, Y> {
+    fn default() -> Self {
+        Self {
+            back: Box::new([[0; X]; Y]),
+            front: Box::new([[0; X]; Y]),
+        }
+    }
+}
+
+impl<const X: usize, const Y: usize> Board<X, Y> {
+    /// Copies a template into the top left corner of the front buffer
+    pub fn copy_from<const AX: usize, const AY: usize>(&mut self, other: [[u8; AY]; AX]) {
+        for (y, other) in other.iter().enumerate().take(Y) {
+            for (x, other) in other.iter().enumerate().take(X) {
+                self.set(x, y, *other);
+            }
+        }
+        self.swap()
+    }
+    /// Sets `(x, y)` to `value` in the back buffer
+    pub fn set(&mut self, x: usize, y: usize, value: u8) {
+        self.back[y][x] = value;
+    }
+    /// Gets the value of `(x, y)` in the front buffer
+    pub fn get(&self, x: usize, y: usize) -> u8 {
+        self.front[y][x]
+    }
+    /// Swaps the front and back buffers
+    pub fn swap(&mut self) {
+        let Self { back, front, .. } = self;
+        std::mem::swap(front, back)
+    }
+    /// sums the immediate neighbors of (cx, dx)
+    pub fn sum_neighbors(&self, cx: usize, cy: usize) -> u8 {
+        let (cx, cy, mut neighbors) = (cx as isize, cy as isize, 0);
+        for dx in -1..=1 {
+            for dy in -1..=1 {
+                if (dx, dy) == (0, 0) {
+                    continue;
+                }
+                let (x, y) = (rem(cx + dx, X), rem(cy + dy, Y));
+                neighbors += self.get(x, y)
+            }
+        }
+        neighbors
+    }
+    /// Evaluates the Game of Life ruleset
+    pub fn life(&mut self, x: usize, y: usize) {
+        let state = match (self.get(x, y), self.sum_neighbors(x, y)) {
+            (0, 2) => 0,     // A dead cell with 2 neighbors dies
+            (_, 2..=3) => 1, // A cell with 2 or 3 neigbors comes alive
+            _ => 0,          // Any other cell dies
+        };
+        self.set(x, y, state)
+    }
+    /// Produces a new generation
+    pub fn update(&mut self) {
+        for y in 0..Y {
+            for x in 0..X {
+                self.life(x, y);
+            }
+        }
+        self.swap()
+    }
+}
+
+impl<const X: usize, const Y: usize> std::fmt::Display for Board<X, Y> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        writeln!(f, "┌{:─<1$}┐", "", X * 2)?;
+        for y in self.front.iter() {
+            "│".fmt(f)?;
+            for x in y {
+                f.write_str(to_str(*x))?;
+            }
+            "│\n".fmt(f)?;
+        }
+        write!(f, "└{:─<1$}┘", "", X * 2)
+    }
+}
+
+/// Gets a little guy if the cell is alive
+fn to_str(cell: u8) -> &'static str {
+    match cell {
+        0 => "  ",
+        _ => "🮲🮳",
+    }
+}
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..c9c8638
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,26 @@
+use std::time::{Duration, Instant};
+
+use game_life::Board;
+
+const W: usize = 22;
+const H: usize = 12;
+// Framerate
+const RATE: f32 = 60.0;
+
+#[allow(unused_mut)]
+fn main() {
+    let mut board: Board<W, H> = Default::default();
+    // Stick a glider in the top left corner
+    board.copy_from([
+        [0, 1, 0],
+        [0, 0, 1],
+        [1, 1, 1],
+    ]);
+    println!("\x1b[H\x1b[J");
+    loop {
+        let time = Instant::now();
+        println!("\x1b[H{board}");
+        board.update();
+        std::thread::sleep(Duration::from_secs_f32(RATE.recip()).saturating_sub(time.elapsed()));
+    }
+}